<title>Reduction of photodegradation in optical fibers for excimer laser applications</title>

Abstract

Power transmission of excimer laser radiation at 308 nm through waveguides is of growing importance in medical applications. The maximum energy densities achievable at distal fused silica optical fiber ends are limited by the surface damage threshold of fused silica and by photodegradation of the optical fiber material. Limitations due to the surface damage threshold at the front surface can be avoided by applying tapered fiber geometries. In order to minimize photodegradation effects colour center formation caused by high energy UV radiation has to be reduced. This involves optimization of the fused silica material properties and the necessity of modifying the manufacturing processes. Measurements on all silica fibers at 308 nm wavelength (XeCl excimer laser) show different influences of core material manufacturing. Not only the overall decrease of transmission but also the dependence of transmission changes on the number of laser pulses and defect annealing are strongly affected. Consequences for improved performance of all silica optical fibers in angioplasty are demonstrated by measurements on specially produced samples.

Low photodarkening single cladding ytterbium fibre amplifier

“…Photodegradation of silica fibre under direct UV irradiation is well known where an increase in background loss under UV radiation occurs 9,10 . When strongly pumping ytterbium fibre with a pump at 977 nm, clusters of three or four ytterbium ions can emit radiation in the UV region.…”